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Questions and Answers
A ______ is an α motor neurone and all the muscle fibres innervated by that neurone.
A ______ is an α motor neurone and all the muscle fibres innervated by that neurone.
motor unit
The relationship between muscle fibres and motor units determines how ______ the control is on that muscle.
The relationship between muscle fibres and motor units determines how ______ the control is on that muscle.
precise
Tetanus in skeletal muscle results in a sustained muscle ______.
Tetanus in skeletal muscle results in a sustained muscle ______.
contraction
During prolonged contraction of a muscle, units ______ so some are contracting while others are not.
During prolonged contraction of a muscle, units ______ so some are contracting while others are not.
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The optimal resting length for the sarcomere is necessary to achieve maximum ______ of contraction.
The optimal resting length for the sarcomere is necessary to achieve maximum ______ of contraction.
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At high levels of stimulation, there is a sustained rise in intracellular ______, allowing for greater force than during a single twitch.
At high levels of stimulation, there is a sustained rise in intracellular ______, allowing for greater force than during a single twitch.
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To increase force of contraction, smaller motor units tend to be recruited ______.
To increase force of contraction, smaller motor units tend to be recruited ______.
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As muscle length increases, there is an increase in ______ developed until a limit is reached.
As muscle length increases, there is an increase in ______ developed until a limit is reached.
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The mechanism of contraction for cardiac muscle is significantly influenced by the cardiac muscle ______ potential.
The mechanism of contraction for cardiac muscle is significantly influenced by the cardiac muscle ______ potential.
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The ______ of contraction of skeletal muscle can be varied by adjusting tetanus and motor unit recruitment.
The ______ of contraction of skeletal muscle can be varied by adjusting tetanus and motor unit recruitment.
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Study Notes
### Muscle Fiber Components
- Muscle fibers are made up of myofibrils, which contain sarcomeres.
- Sarcomeres are the functional units of muscle fibers.
- Sarcomeres are made up of thin filaments (actin) and thick filaments (myosin).
- Thin filaments are attached to the Z-disc.
- Thick filaments are attached to the M-line.
### Relationship Between Resting Length and Force Generation
- The resting length of a muscle fiber affects the force it generates when it contracts.
- The optimal resting length for a sarcomere is when there is maximal overlap between actin and myosin filaments.
- Overstretching a sarcomere reduces the overlap between actin and myosin filaments, decreasing force generation.
### Force/Strength of Contraction
- Tetanus/Tetany: Sustained muscle contraction due to high levels of stimulation and sustained rise in intracellular calcium.
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Motor Unit Recruitment: Motor units consist of an α motor neuron and all the muscle fibers it innervates.
- Larger motor units result in less precise control.
- Smaller motor units are typically recruited first for weaker contractions.
- As more force is needed, larger motor units are recruited.
- During prolonged contraction, motor units alternate to prevent fatigue.
### Length-Tension Curve
- The length-tension curve demonstrates the relationship between sarcomere length and force generated.
- A shortened sarcomere doesn't generate as much force.
- Optimal resting length of a sarcomere generates the maximum force.
- A lengthened sarcomere will have reduced force due to less overlap between actin and myosin filaments.
### Cardiac Muscle
- The cardiac muscle action potential is important for muscle contraction because it allows for a longer refractory period, preventing tetany.
- Calcium ions play a crucial role in activating the contractile proteins in cardiac muscle.
### Smooth Muscle
- Smooth muscle contraction is initiated by calcium ions, which activate myosin light chain kinase.
- Myosin light chain kinase phosphorylates myosin, allowing it to bind to actin and initiate contraction.
### Key Differences
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Skeletal muscle: Voluntary, striated, multinucleated
- Rapid contraction, can generate large force
- Utilized for movement, posture, and breathing
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Cardiac muscle: Involuntary, striated, uninucleated
- Responsible for the beating of the heart
- Has a longer refractory period to prevent tetany
-
Smooth muscle: Involuntary, non-striated, uninucleated
- Found in the walls of internal organs, blood vessels, and airways
- Slower contraction, can sustain contraction for long periods
- Regulates blood pressure, digestion, and respiration
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Description
Explore the components of muscle fibers and their functional units, sarcomeres. Understand the relationship between resting length, force generation, and the concepts of tetanus and motor unit recruitment. This quiz covers essential muscle physiology principles.
